Machines for the formation of the longitudinal seam of a necktie generally are intended to form this seam along the backside of the necktie.
For this purpose, an extremely long flexible needle is used since the needle must pass through the entire length of the necktie along the seam which is formed until it emerges from the opposite end of the necktie. As a consequence, the needle comprises a needle point and a wire connected to the needle point so that the needle point can be said to be formed at one end of the wire.
The wire is wound up on a needle spool and is initially unrolled to move the needle point to the opposite side of the machine.
When the needle point arrives at this opposite side, the needle point is guided into a needle abutment screw which forms part of a threading arrangement coacting with the needle point so that a part can move with the needle point until the needle point reaches a predetermined position at which a yarn is threaded into the needle eye.
The construction of the threading device, because of the need to guide the yarn with precision into the needle eye, is therefore relatively complex.
For a variety of reasons, however, the needle eye does not always lie at the precisely required angle to the threading device. This angular misalignment may be a result of an inaccurate welding of the needle point onto the wire, some damage to the wire or to the needle point or a consequence of a twisting of the needle point resulting from its engagement with the material to be sewn.
As a consequence, a yarn may not be threaded into the needle eye accurately every time. Only when a yarn has been properly threaded into the needle eye is a completion signal given so that the needle can return and the seam made.